1. Field of the Invention
This invention relates generally to photo-reproduction and more specifically to the field of flow cameras that are operable to make miniaturized film images of wide or long originals as a prelude to digital scanning or projection of the film image using conventional photographic techniques and equipment. The flow camera photographs large original documents as they are moved continuously past the camera lens.
The invention in part relates to a flow camera having aperture adjustment mechanism which permits selective fine adjustment of the camera aperture from outside of the housing, and which is functional to allow aperture adjustment to be accomplished during photographing of a document. In addition, the invention concerns a flow camera having improved light means for illuminating the document during photographing, along with novel baffle means which allows only light reflected directly from the document to enter the image path to the camera. The invention further relates to improved detectors for precisely detecting entry of a document into the flow path of the flow camera and which serve to enhance correlation of document entry with initiation of movement of the roll, and to interrupt film movement after the image on the document has been fully photographed.
2. Description of the Prior Art
Flow cameras constructed in accordance with the teachings of U.S. Pat. No. 5,341,192, hereby incorporated by reference, represent a distinct advance in the state of the art of flow cameras. As those skilled in the art appreciate, such flow cameras allow the photographing for archival purposes of large documents such as drawings used in the manufacture of aircraft, automobiles and ships and in the fields of petroleum, right-of-way maintenance, seismology, and other similar large sized documents.
As alluded to in the '192 patent, even the largest film-making cameras with huge subject holders for displaying originals to an objective lens usually have two principle limitations. First, they are slow and cumbersome to load and unload. Second, they have a finite, maximum size for originals that can be reproduced. Long originals can only be done in sections. Flow cameras on the other hand, are easy to load and will accommodate originals of any length because they operate while the original is in motion, or "on the fly" so to speak. Flow cameras are much faster than a regular camera with a framed subject holder. More importantly, a flow camera can make a one-film image from an original of virtually any length.
Only a few miniaturizing filming cameras have ever been offered commercially, using either the flow principle or large stationary subject holders. This is believed to be attributable to the conceptual complexity of the requisite hardware, the difficulty in fabricating the equipment, the lack of effective control over the reproduction process, and the disparity in numbers between large and small originals requiring reproduction. There are only a small number of originals in the 4 to 30 feet category for example which require reproduction, while there are a much larger number of originals with shorter lengths. Economic considerations have therefore in large measure restricted development work on cameras capable of reproducing very large drawings on film. That fact however does not mean there is no need for a camera which can film long originals, and that at the same time, may be unusually wide. Long drawing roll lengths with widths of from 50 to 54 inches are not uncommon. Flow cameras can be easily scaled up to shoot 60 inches or more in width. The flow camera also offers optical advantages that cannot be matched in a conventional camera for reproducing long, large scale, and particularly long length drawings.
A flow camera as shown and described in the '192 patent introduced a feature wherein means was provided for lighting originals on both the front and back simultaneously. This resulted in making congruent images on the backs of the drawings available to the objective lens so that both front and back became part of the finished imagery. Lighting beneath the back of the document being reproduced also had the effect of sharpening the image of the front side of the drawing or the side facing the lens. However, under certain conditions of actual use of the '192 patent flow camera, an occasional aberration was detected in the form of double images or blurred images. These aberrations were particularly troublesome while filming certain types of original copy such as clear film positives of topography and seismic sections which contained a profusion of fine, thin lines. Localized blurring also tended to manifest itself in continuous tone photogrammetry like aerial strip maps.
These aberrations persisted even when the masking slit through which the image passed was adjusted to the minimum transverse width of about 12.7 mm in the center to about 19.05 mm at the ends of the slot longitudinally.
Empirically it was determined that light rays from the two top lights as used in the '192 patent camera, crossing in both directions underneath the exposure slit, in certain instances allowed light rays to bounce back off of originals, particularly those that had a glossy appearance, during the instant that the original was passing under the optical axis. It was found that even if the masking slit through which the image was viewed by the lens was reduced to as little as 9.5 mm, undesirable light bounce still occurred.
Many large originals advantageously requiring reproduction had characteristics which facilitated making image aberrations noticeable. They tended to have overall repetitive patterns which, if interrupted, showed obvious blemishes. These flaws were especially noticeable where the image covered most of the area, thus making any faults in the reproduction clearly evident.
Prior art flow cameras also presented problems with the numerous optical sensors used to detect documents as they passed through the transport mechanism of the camera. Two rows of these optical sensors were used to detect entry and exit from the exposure area.
Another problem with prior art flow cameras was the difficulty in changing the aperture of the objective lens of the camera. This required opening the housing in darkness and then removing and storing the unexposed film. Next, certain components had to be removed around the lens to gain access to the aperture and the aperture then adjusted. Finally, this process had to be reversed to reassemble the camera.
Flow camera operators were well aware of the time consuming nature of the aperture adjustment process. Even if the time was available though, some documents require adjustment during the filming process of a single document and such an adjustment is not possible with existing flow cameras.